Electrical stimulation is generally the application of an electrical current to a load using a current source or a voltage source. A voltage source has a low output impedance and provides a constant voltage and variable current, while a current source has a high output impedance and provides a constant current and variable voltage. In applications where the load is neural tissue, traditionally, a constant current source has been used to deliver a known constant current in the presence of a constantly changing tissue resistance. However, application of the constant current can lead to an accumulation of charge at the tissue-electrode interface, which can cause irreversible electrochemical reactions that can damage the tissue or the electrode.